LOS ANGELES — A shooting that left two men dead at UCLA on Wednesday and led to a massive response on the campus in a bustling part of Los Angeles was a murder-suicide, authorities said.

Police Chief Charlie Beck declared the campus safe about two hours after authorities received a 911 call. The shooting happened in a small office in an engineering building called Boelter Hall, and a gun was found along with what might be a suicide note, he said. No names have been released.

Hundreds of officers from multiple federal and local agencies swarmed the campus, which had been placed on lockdown. Teams in tactical gear looking for victims and suspects ran across campus, some with weapons drawn, and stormed into buildings. People emerged from buildings with their hands raised or behind their heads.

The shooting occurred the week before final exams at UCLA, a major campus of the University of California system with about 43,000 students.

Many students posted to social media, many to let friends and family know they were safe. Some described frantic evacuation scenes and a large police response. Others wrote that their doors weren’t locking and posted photos of items like photocopiers and foosball tables pushed up against them.

The focus of police activity was a cluster of engineering buildings near the center of a campus that occupies 419 acres in Los Angeles. At a mathematical sciences building near Boelter Hall, SWAT officers with guns drawn cleared occupants who emerged one by one.

One man walked out with his hands up and was told to get on his knees. An armed officer searched him and his backpack, then sent him on his way with his hands still in the air.

Bioengineering professor Denise Aberle said she could see “a lot of police activity with innumerable cars” and a police helicopter hovering over the engineering building.

“Police keep coming,” she said.

Associated Press writers Amanda Lee Myers, Christine Armario and Justin Pritchard in Los Angeles and Alina Hartounian in Phoenix contributed to this report.